1. Field of the Invention
This invention relates to a fuel injection control system, a fuel injection control method, and an engine control unit, for an internal combustion engine which is capable of changing at least one of the cam phase of each intake cam and that of each exhaust cam, relative to a crankshaft of the engine, to thereby change a valve overlap period during which both the intake valve and the exhaust valve are open, the fuel injection control system controlling the amount of fuel injected into the engine.
2. Description of the Prior Art
Conventionally, a fuel injection control system of the above-mentioned kind was proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 2000-179381. The engine incorporating the disclosed fuel injection control system includes a cam phase change mechanism. The cam phase change mechanism is of a hydraulically driven type which is supplied with hydraulic pressure so as to change a cam phase, which is indicative of an amount of advancement of an intake cam shaft relative to an exhaust cam shaft, such that the cam phase becomes equal to a target cam phase. In the process, since the cam phase change mechanism is hydraulically driven, the cam phase does not change instantaneously, but changes progressively toward the target cam phase with a response delay. To overcome the problems resulting from this response delay, in this fuel injection control system, when the engine is in a transitional operating condition from a high-load operation to a low-load operation during deceleration, an injection amount-increasing coefficient for increasing the fuel injection amount is calculated in the following manner: An actual load on the engine is calculated based on the intake pipe pressure, and a target load on the same is calculated based on the opening degree of a throttle valve and the rotational speed of the engine. Then, it is determined based on the difference between the calculated actual load and target load whether or not the engine is in a transitional operating condition from a high-load operation to a low-load operation. Further, it is determined whether or not the cam phase is in a transitional state for decreasing toward the target cam phase for the low-load operation of the engine (i.e. changing in a retarding direction). If the engine and the cam phase are both in the respective transitional condition and transitional state, the injection amount-increasing coefficient is calculated, based on the engine rotational speed, the actual load, and the cam phase, according to an increase in the amount of intake air. Then, an increase in the fuel injection amount is controlled by using the injection amount-increasing coefficient. Thus, the problems caused by the delay in response of the cam phase change mechanism, including a stall and a misfire of the engine, are prevented, and stable combustion is maintained.
In the above internal combustion engine, the response delay of the cam phase change mechanism causes the cam phase to continuously decrease toward the target cam phase in the retarding direction even during an intake stroke, to thereby reduce the valve overlap period during the intake stroke, whereby an internal EGR amount (remaining gas quantity) is reduced. As a result, the temperature of an air-fuel mixture falls, resulting in a decrease in the temperature of the wall surface of intake ports, which causes an increase in the amount of fuel adhering to the wall surface of the intake port. Further, the decrease in the valve overlap period means an increase in a substantial or effective valve-opening time period of the intake valve, which causes an increase in the amount of intake air. The above changes in the state of the air-fuel mixture within a combustion chamber are conspicuous especially when the difference between the cam phase and the target cam phase is large. In the above fuel injection control system, however, since the injection amount-increasing coefficient is calculated simply based on the engine rotational speed, the actual load, and the cam phase, the fuel injection amount cannot be properly controlled in response to the changes in the state of the air-fuel mixture caused by the continuous decrease in the cam phase in the retarding direction during the intake stroke, which causes deviation of the air-fuel ratio of the air-fuel mixture from a target air-fuel ratio. This can result in a lowered engine output, increased emissions and decreased fuel economy, and hence makes it impossible to provide adequate engine performance. Further, the above-described conventional fuel injection control system performs the above control only when the cam phase is on the decrease, but cannot perform control when the cam phase is on the increase.
It is an object of the invention to provide a fuel injection control system, a fuel injection control method, and an engine control unit, for an internal combustion engine which is capable of accurately controlling the fuel injection amount in response to a change in a valve overlap period due to a change in a cam phase, thereby ensuring excellent engine performance.
To attain the above object, according to a first aspect of the present invention, there is provided a fuel injection control system for an internal combustion engine including intake valves, intake cams for opening and closing the intake cams, respectively, exhaust valves, exhaust cams for opening and closing the exhaust cams, respectively, and a crankshaft connected to the intake cams and the exhaust cams, the engine being capable of changing at least one of a cam phase of each intake cam and a cam phase of each exhaust cam, relative to a crankshaft of the engine, to thereby change a valve overlap period, and causing fuel injection toward intake ports of the engine.
The fuel injection control system according to the first aspect of the invention is characterized by comprising:
valve overlap change amount-detecting means for detecting an amount of change in the valve overlap period;
wall surface temperature-detecting means for detecting a wall surface temperature of the intake ports;
operating condition-detecting means for detecting operating conditions of the engine;
fuel injection amount-setting means for setting a fuel injection amount according to the detected operating conditions; and
fuel injection amount-correcting means for correcting the set fuel injection amount according to the detected amount of change in the valve overlap period and the detected wall surface temperature of the intake ports.
In this fuel injection control system, when the valve overlap period is changed due to a change in the cam phase, the fuel injection amount is set according to the detected operating conditions of the engine, and then the fuel injection amount thus set is corrected according to the amount of change in the valve overlap period and the wall surface temperature of the intake ports. In this case, the amount of change in the valve overlap period is a parameter in which changes in an internal EGR amount and the amount of intake air due to the change in the valve overlap period are reflected, while the wall surface temperature of the intake ports is a parameter in which a change in the amount of fuel adhering to the wall surface of the intake port, due to the change in the valve overlap period is reflected. Therefore, by correcting the fuel injection amount according to these parameters, it is possible to accurately control the fuel injection amount by reflecting the changes in the internal EGR amount, the amount of intake air, and the amount of fuel adhering to the wall surface, due to a continuous or progressive change in the valve overlap period, whereby appropriate engine performance dependent on the actual state of an air-fuel mixture within the combustion chamber can be achieved. It should be noted that throughout the present specification, xe2x80x9cdetection of the amount of change in the valve overlap periodxe2x80x9d and xe2x80x9cdetection of the wall surface temperature of the intake portsxe2x80x9d include not only detections performed directly by sensors, but also estimations by arithmetic operations.
Preferably, the fuel injection control system further comprises atmospheric pressure-detecting means for detecting an atmospheric pressure, and second fuel injection amount-correcting means for correcting the fuel injection amount according to the detected atmospheric pressure.
In general, with a change in the atmospheric pressure, back pressure on the exhaust side of the engine changes, which causes a change in the amount of gas remaining in the combustion chamber and a resultant change in the amount of intake air. In short, the atmospheric pressure is a parameter in which the change in the amount of intake air is reflected. According to this preferred embodiment, the fuel injection amount is corrected according to the atmospheric pressure, whereby the fuel injection amount can be properly calculated by reflecting the change in the amount of intake air due to the change in the atmospheric pressure. This enables further accurate control of the fuel injection amount.
Preferably, the fuel injection amount-correcting means corrects the fuel injection amount such that when the amount of change in the valve overlap period shows an increase in the valve overlap period, the fuel injection amount is reduced, whereas when the amount of change in the valve overlap period, shows a decrease in the valve overlap period, the fuel injection amount is increased.
When the valve overlap period is on the increase, the internal EGR amount is increasing and the amount of intake air is decreasing, and when the valve overlap period is on the decrease, the internal EGR amount is decreasing and the amount of intake air is increasing. According to this preferred embodiment, when the amount of change in the valve overlap period shows an increase in the valve overlap period, the fuel injection amount is corrected such that it is decreased, which enables more accurate control of the fuel injection amount. On the other hand, when the amount of change in the valve overlap period shows a decrease in the valve overlap period, the fuel injection amount is corrected such that it is increased, which also enables more accurate control of the fuel injection amount.
To attain the above object, according to a second aspect of the invention, there is provided a fuel injection control system for an internal combustion engine including intake valves, intake cams for opening and closing the intake cams, respectively, exhaust valves, exhaust cams for opening and closing the exhaust cams, respectively, and a crankshaft connected to the intake cams and the exhaust cams, the engine being capable of changing at least one of a cam phase of each intake cam and a cam phase of each exhaust cam, relative to a crankshaft of the engine, to thereby change a valve overlap period, and causing fuel injection toward intake ports of the engine.
The fuel injection control system according to the second aspect of the invention is characterized by comprising:
a valve overlap change amount-detecting module for detecting an amount of change in the valve overlap period;
a wall surface temperature-detecting module for detecting a wall surface temperature of the intake ports;
an operating condition-detecting module for detecting operating conditions of the engine;
a fuel injection amount-setting module for setting a fuel injection amount according to the detected operating conditions; and
a fuel injection amount-correcting module for correcting the set fuel injection amount according to the detected amount of change in the valve overlap period and the detected wall surface temperature of the intake ports.
According to the second aspect of the invention, the same advantageous effects as provided by the first aspect of the invention can be obtained.
Preferably, the fuel injection control system further comprises an atmospheric pressure-detecting module for detecting an atmospheric pressure, and a second fuel injection amount-correcting module for correcting the fuel injection amount according to the detected atmospheric pressure.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the fuel injection amount-correcting module corrects the fuel injection amount such that when the amount of change in the valve overlap period shows an increase in the valve overlap period, the fuel injection amount is reduced, whereas when the amount of change in the valve overlap period shows a decrease in the valve overlap period, the fuel injection amount is increased.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
To attain the above object, according to a third aspect of the invention, there is provided a fuel injection control method for an internal combustion engine including intake valves, intake cams for opening and closing the intake cams, respectively, exhaust valves, exhaust cams for opening and closing the exhaust cams, respectively, and a crankshaft connected to the intake cams and the exhaust cams, the engine being capable of changing at least one of a cam phase of each intake cam and a cam phase of each exhaust cam, relative to a crankshaft of the engine, to thereby change a valve overlap period, and causing fuel injection toward intake ports of the engine.
The fuel injection control method according to the third aspect of the invention is characterized by comprising the steps of:
detecting an amount of change in the valve overlap period;
detecting a wall surface temperature of the intake ports;
detecting operating conditions of the engine;
setting a fuel injection amount according to the detected operating conditions; and
correcting the set fuel injection amount according to the detected amount of change in the valve overlap period and the detected wall surface temperature of the intake ports.
According to the third aspect of the invention, the same advantageous effects as provided by the first aspect of the invention can be obtained.
Preferably, the fuel injection control method further comprises the steps of detecting an atmospheric pressure, and correcting the fuel injection amount according to the detected atmospheric pressure.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the step of correcting the fuel injection amount includes correcting the fuel injection amount such that when the amount of change in the valve overlap period shows an increase in the valve overlap period, the fuel injection amount is reduced, whereas when the amount of change in the valve overlap period shows a decrease in the valve overlap period, the fuel injection amount is increased.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
To attain the above object, according to a fourth aspect of the invention, there is provided an engine control unit including a control program for causing a computer to carry out fuel injection control for an internal combustion engine including intake valves, intake cams for opening and closing the intake cams, respectively, exhaust valves, exhaust cams for opening and closing the exhaust cams, respectively, and a crankshaft connected to the intake cams and the exhaust cams, the engine being capable of changing at least one of a cam phase of each intake cam and a cam phase of each exhaust cam, relative to a crankshaft of the engine, to thereby change a valve overlap period, and causing fuel injection toward intake ports of the engine.
The engine control unit according to the fourth aspect of the invention is characterized in that the control program causes the computer to detect an amount of change in the valve overlap period, detect a wall surface temperature of the intake ports, detect operating conditions of the internal combustion engine, set a fuel injection amount according to the detected operating conditions, and correct the set fuel injection amount according to the detected amount of change in the valve overlap period and the detected wall surface temperature of the intake ports.
According to the fourth aspect of the invention, the same advantageous effects as provided by the first aspect of the invention can be obtained.
Preferably, the program further causes the computer to detect an atmospheric pressure, and correct the fuel injection amount according to the detected atmospheric pressure.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, in correcting the fuel injection amount, the program causes the computer to correct the fuel injection amount such that when the amount of change in the valve overlap period shows an increase in the valve overlap period, the fuel injection amount is reduced, whereas when the amount of change in the valve overlap period shows a decrease in the valve overlap period, the fuel injection amount is increased.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.